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Why isn't the moment always included in a free-body diagram?

Now I have seen many times both in my physics book and other books when drawing a free body diagram the moment is not included but the forces are. For example in 2d when a beam is fixed to a wall ...
per persson's user avatar
0 votes
2 answers
111 views

What is the connection between moments in probability theory and the moment of inertia?

My question arises as the moment of inertia (MOI) has been described as a second moment. In my understanding if the MOI is indeed a second moment of a distribution of mass, this suggests the MOI could ...
Luke K's user avatar
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Mass moment of inertia flipping in different mediums

Consider someone performing a front flip in the water versus in the air. Assume the body position in both cases to be identical. In which case would the mass moment of inertia be greater and why? Prof ...
user401506's user avatar
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24 views

Average Energy and Magnetization of One Site Hubbard Model

I have been trying to implement the exercises from Section 2 part B (for which $t = 0$, and only considering the effects of U) given in this set of lecture notes - Numerical Studies of Disordered ...
CuriousMind's user avatar
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1 answer
100 views

Calculate bending moment for cantilever with uniformly distributed load

I am trying to understand how to calculate the bending moment for a cantilever with a uniformly distributed load so that I can build an equation of moments, as shown in this example: I tried ...
eheshing's user avatar
0 votes
1 answer
328 views

Moment of inertia of a cantilever beam [closed]

As part of a project, I'm calculating deflection of a cantilever beam, something like the image below where the beam bends due to a load. To do so requires its moment of inertia, and I'm thinking of ...
Rena W's user avatar
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2 answers
76 views

Misconception About Torque Log cutting example

LOG CUTTING "Three friends go camping in the forest with their families. They start collecting wood to make a fire. They find a large, branchless log in the forest. One end of the log is very ...
AliceX's user avatar
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1 vote
3 answers
100 views

Sign of distance/arm when finding moment/torque

I know that $M=Fd$, but when I have a negative moment, does the sign of the moment matter when I'm calculating for distance? If yes, then what would it mean when distance is negative?
user16629503's user avatar
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2 answers
72 views

i've been told that a motor bike can turn on a frictionless horizontal surface by leaning towards the horizontal

their reasoning was that when the bike lean towards horizontal the reaction acting on the bike by surface will act in an angle through the center of gravity of the slanted bike(not perpendicular to ...
cannister super's user avatar
0 votes
2 answers
407 views

Difference between moment and couple

What is the exact difference between a moment and a couple? In some YouTube channels and books, they say the moment of a force produces a translational as well as rotational motion whereas the concept ...
ARAVINDHAN GK's user avatar
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0 answers
68 views

Underwater chests in video games

Many video games creators put chests with items in various places. Sometimes the chests can be found underwater. Here are two examples: Dying Light 2 Shadow of the Tomb Raider However, I started ...
Lukasz Skowron's user avatar
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0 answers
33 views

What is the most fundamental reason for introduction of force moment $\vec{M}=\vec{r}\times\vec{F}$? [duplicate]

Force moment is defined as $\vec{M}=\vec{r}\times\vec{F}$ when force is perpendicular to the lever arm. How do we know that it has to be this way? How do we know it is not $F\cdot r^2$ etc. ? My ...
Lukasz Skowron's user avatar
18 votes
3 answers
4k views

How does a lever arm increase force?

A lever and a fulcrum is able to to multiply the input force to the output force and trade moving distance for increased force. The same happens in automobile transmissions, taking advantage of high ...
Erik's user avatar
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1 vote
3 answers
183 views

Why does moment/torque equal to force multiplied by distance?

moment is equal to force x distance but why is is it so. why is it so that greater the distance less the effort needed? i tried understanding it mathematically but it just went over my head. if any ...
user366794's user avatar
3 votes
3 answers
1k views

How do you apply a pure torque?

A pure torque does not have a point of application. For example, in the beam shown below, the reactions are same regardless of the torque placement: But how do you apply torque in reality? For ...
user355019's user avatar
5 votes
1 answer
373 views

If torque is a form of moment, then why is the word 'moment' used for the 'magnetic dipole moment', NiA, for a current-carrying loop?

I thought torque is a form of moment: If the moment makes the object rotate, we call it torque; otherwise we just use the name moment. However it seems the electric & magnetic dipole moments are ...
across's user avatar
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0 votes
2 answers
52 views

Maintaining the balance of a rod of uniform density [closed]

Assume a rod which: is of uniform density $\rho$. is a metre long. The rod is balanced on a knife edge at 58 cm. mark (in the notation where the extreme left side is assumed to be 0). To the extreme ...
mnuizhre's user avatar
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1 answer
208 views

How non-collinear forces balance each other?

In the system of parallel forces , all the forces are non-colinear. So how to they balance each other?. Here in this case a wooden plank is supported at its end by two supports. All the forces here ...
user avatar
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4 answers
618 views

Are there physics theorems that can prove maths theorems? Eg Pythagoras' Theorem

There's this recent post on maths overflow Which theorems have Pythagoras' Theorem as a special case? that has an answer by dxiv that appears to use a physics theorem to a prove a maths theorem, ...
BCLC's user avatar
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-1 votes
1 answer
36 views

Are these two torques identical? [closed]

Hello, I had this question in a MCQ. According to the solution, these torques are indeed identical but I don't understand how. I tried to decompose $\overrightarrow{AB}$ into $\overrightarrow{AC} + \...
YazidH94's user avatar
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1 answer
44 views

Why do references use different variables in the differential of moment of inertia?

I see formulas in moment of inertia that use mass, area or volume as the differential in moment of inertia. I do not have a good grasp of the concept. The variation in formulas just confuse me. Can ...
AndroidV11's user avatar
3 votes
4 answers
917 views

Why don't simple machines change the amount of energy needed?

Suppose I wanted to tighten a nut and I do so using two spanners of different arm lengths, say of $10 \text{ cm}$ and $20 \text{ cm}$. According to a an online source: A spanner counts as a simple ...
Shane's user avatar
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0 votes
2 answers
1k views

The moment of inertia of a hollow cylinder is lower than that of the "corresponding" solid cylinder (same density, outer radius, height):

This is a self-answered "question" for those scratching their heads after learning, e.g. in class, that the moment of inertia of a hollow cylinder is higher than that of solid cylinder. Note ...
Felix Tritschler's user avatar
0 votes
1 answer
41 views

Best place to shoot an object to topple it

Imagine a carnival game, the ones where you have to shoot down items with a toy gun, my question is where to shoot the item to maximize the rotational moment of the item. My studies lead me to believe ...
Nigel Tan's user avatar
0 votes
1 answer
112 views

Why does a long, free-to-move object rotate when I push it from one side?

I was pushing a pencil along a table top when I noticed that it rotates around the other end. Somewhat like this(The dotted red lines show the final position of the pencil). The pencil is not pivoted ...
AltercatingCurrent's user avatar
0 votes
1 answer
355 views

Why does it matter where you take moments, when its a lamina?

I've just been doing moments on laminas for the first time and I think I've missed something crucial. If I take moments around point $X$, I get: Clockwise: $30\ \mathrm N$ with a perpendicular ...
harpomiel's user avatar
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0 votes
1 answer
228 views

Question about moment with two springs and one weight

The answer to this question is C. I got to it by realizing that if the weight is moved away from the pivot then it will produce an anti-clockwise moment which will cause X to decrease and Y to ...
moonyy.'s user avatar
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0 answers
38 views

Meaning of torque

So, in the diagram, A is the axis of rotation and the net moment from the forces acting there(as shown) is 6Nm.The moment is due to the forces acting in the direction as shown and the moment the ...
Lime's user avatar
  • 87
0 votes
1 answer
65 views

Why does rotation happens about hinge point in a vertical bar when net force acting on it are zero? [closed]

As we know that if the net external force on a body is zero its center of mass will be at rest and also rotation will happen about center of mass only but in this hinge and rod case it is clear by ...
HIMANSHU KUMAR's user avatar
-1 votes
1 answer
249 views

Sliding arm problem, locking and singularity

I posted a version of this earlier but I feel like my problem was not very clear so I hope that this explains what is so confusing here. Shown in the image is a view from above, of an arm that's ...
karl's user avatar
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4 votes
2 answers
691 views

Why does a body rotate faster if force is applied away from the pivot?

Why does a body rotate faster if force is applied away from the pivot? I need an intuitive answer to this. Like why does a door rotate slower if I push at it closer to its hinge, or faster if I push ...
Jirhs Kumar 's user avatar
-1 votes
1 answer
2k views

How to determine the direction of moments (confusion)?

My teacher is showing me a few ways that I can calculate moment and its direction. In this example, she is going to use the principle of moments to solve this (ie resolving into components) But what ...
CountDOOKU's user avatar
1 vote
1 answer
1k views

How is the "wrench" a simplification for a general force-couple system? [closed]

from engineering mechanics, by beer and johnston For any system of n forces, we can simplify this system to a Force-Couple system. The simplification is intuitive- we don't need lot of forces just a ...
ark's user avatar
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0 votes
0 answers
52 views

Is there a system that only contains electric dipole moment but not higher electric multipole moments?

Does there exist such thing, if it does, which charge distribution could generate it? If it doesn't exist, can it be proven?
mind's user avatar
  • 11
1 vote
1 answer
80 views

Are there higher moments of vector quantities?

The $n$-th moment of mass of a point mass $m$ with respect to a point located at $\boldsymbol r$ is $$ \mu_n(m) = m\boldsymbol r^n $$ So the 0th moment is the total mass $m$, the 1st moment is $m\...
Pato Raimundo's user avatar
2 votes
1 answer
325 views

Overturning torque on a car navigating a curve

The car shown above with mass M is turning to the left with an uniform angular speed W on a circular path with radius R. When the angular speed is increased to a critical value C, one of the normal ...
tangolin's user avatar
  • 133
-1 votes
3 answers
1k views

How is there moment for a group of forces which its resultant equals zero?

I am a beginner in mechanics, and when I was introduced to moments there was a theorem that says "if a set of forces acting on a rigid body has a resultant, then the algebraic sum of these forces ...
Eman's user avatar
  • 29
15 votes
4 answers
2k views

Dipole Moment: what does it really represent?

Wikipedia gives the most general expression for the $n^{\rm th}$ moment $\mu_n$ of a physical quantity $\Lambda$ as: $$ \mu_n = \int {\bf x}^n \space \delta({\bf x}) \space \rm d^3 x$$ provided that ...
ric.san's user avatar
  • 1,644
1 vote
2 answers
284 views

What exactly is moment? Why does it correspond to a rotation?

Wikipedia says: Moment is an expression involving the product of a distance and physical quantity. I don't quite get it. Moment is a vector, the cross product of the distance vector and the vector ...
Triet Vo Nguyen Minh's user avatar
0 votes
1 answer
317 views

Moments by normal stress

I am a bit confused with the following formula why is that the normal stress ($z$), not the normal stress ($x$), is involved in the formula for the moment around $x$, $Mx$? Likewise, My also equals ...
PJerk's user avatar
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1 vote
0 answers
32 views

What is mass moment? [duplicate]

My teacher gave the following definition while teaching chapter "Center of mass": "It is defined as the product of mass of the particle and distance of particle from point about which ...
Noobie's user avatar
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2 votes
2 answers
177 views

Does "moment" have a single meaning in physics?

I am a high school student and I am curious about the word moment and what it means in different contexts, whether it has a definite meaning or not? I know it has some relation to different kinds of ...
Archit Chhajed's user avatar
2 votes
4 answers
1k views

What are the proper definitions of moment, couple, torque, 'moment of force'?

When I read some scientific articles I am getting confused with the interchange being used between Torque, Couple, Moment, 'Moment Of Force'. Have I got this correct? Moment is supposed to be some ...
Dubious's user avatar
  • 121
1 vote
1 answer
218 views

Is the angular acceleration of a rigid body independent of the reference point?

I'm solving this particular question (refer to image) in which a rod is released from equilibrium after one of the two springs to which it is initially connected is disconnected. In order to calculate ...
sidsr003's user avatar
1 vote
2 answers
220 views

Why does the Larmor precession frequency depend on $\vec{B}$ instead of $\vec{H}$?

From what I know: The magnetic field strength, $\vec{H}$, is the field generated by a free current flowing on an electric conductor. The magnetic flux density, $\vec{B}$, is a response of the medium ...
Kinka-Byo's user avatar
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1 vote
0 answers
92 views

Intuition behind First moment of area and link to centroids

I essentially have the same question, however only concerning the First moment, as this user ,however none of the answers satisfy my questions. I understand that we are trying to get a sense of the ...
realanswers's user avatar
0 votes
2 answers
108 views

A problem about moment (torque ) [closed]

Everybody knows that moment of a force increases with distance. However, there is a problem about it that makes me confused these days: Let's take a look at this picture due to the formula M = F.d, ...
Fizzics's user avatar
  • 59
0 votes
2 answers
2k views

Physical meaning of internal bending moment

Here's the setup: The textbook, where this is from, first walks through how to find the strain and stress as a function of z, which is fairly straightforward. Then, it calculates the "total internal ...
StormRyder's user avatar
1 vote
1 answer
185 views

When calculating first moments of mass in cylindrical coordinates, can we use $r,\theta$ instead of $x,y$?

Usually when we want to find the center of mass of a 3D body, we need to find the first moments of mass about $x,y,z$, call them $M_x,M_y,M_z$. Defined by $$ M_x = \iiint x\rho \ dV, $$ where $\rho$ ...
Jean's user avatar
  • 113
0 votes
1 answer
998 views

Finding distance of forces for maximum bending moment

I'm having a hard time looking for the distance ($x$) on which the forces must be located for a maximum bending moment. The reaction forces in $A$ and $B$ are dependant of the value of $x$, and so ...
steadrin's user avatar